Temporal Bone Trauma

Temporal Bone Trauma Overview

We are going to switch gears in a big way and hit up the temporal bone for the next four lectures.

And I'm gonna start with temporal bone trauma. I'm gonna use it as an opportunity to just review CT temporal bone anatomy.

We will talk about how we detect fractures, what makes us suspicious of fractures are there, we'll talk about the various ways of classifying fractures, and then we'll wrap up with associated injuries and the various complications that occur in the setting of temporal bone trauma.

CT Temporal Bone Anatomy Review

When I look at temporal bone scans and when I teach trainees, I try to find, we're bombarded with so much imaging now, there's so many series that we get on a pack station, and some of these exams, especially with thin sections, there's so many images.

So I find it's useful to find a few stereotypic levels and concentrate on those.

And then you can kind of look for them and make sure that the major anatomic structures are intact.

So, in the axial plane, I've sort of identified a stereotypic superior, middle and inferior axial image to focus on.

And the same thing in the coronal plane, anterior, middle, and posterior.

So I wanna use those as a way to review the anatomy.

Axial Plane Anatomy

So this is a stereotypic axial top image.

And it has the most recognizable temporal bone structure that everybody knows.

And that's the ice cream cone of the malus and inus within the EpiPen of the middle ear cavity.

When you look posterior to that, you typically see a triangle triangular shaped airspace, which is the mastoid antrum.

It's essentially the dominant air cell within the mastoid cavity.

And it connects to the middle ear cavity through an airway not demonstrated on here called the Aus.

At antrum, you see a portion of the int and pad facial nerve canal.

And I'll review that separately on its own.

And other structures you'll see in the inner ear are portions of the cochlea and the vestibule.

You will see the oval window, which I think is better evaluated a little bit more inferiorly.

And then in the coronal plane, moving to a middle axial image, approximately middle, you can see the malus neck.

The malus is the most anterior ossicle.

So ossicular structures that you see more anteriorly are likely to be part of the malus.

You see sort of a conglomerate shadow of the long and lenticular processes, portions of the distal inus in this plane.

The Incas is better seen on the coronal plane.

And then you should be able to see on your imaging as a routine the Staes really to this level at this point.

I use that as a kind of hallmark of whether my scans are of reasonable quality or not.

I think in the when I trained, we all sort of hallucinated that.

They're like, oh, there's the anterior cruise, here's a posterior cruise.

And I was like, oh, yeah, yeah, whatever you say.

But now I think with our multi detector scanners and very thin images, we can expect to see the stape well, and it's a very recognizable structure, anterior and posterior cura, the Capella and the nplate, which sits on the oval window.

Now, at the bottom of your axial images, you should expect to see two parallel lines.

Again, the more anterior one represents a portion of the mals, it's the more anterior osci.

And then posteriorly, again, you're gonna see kind of a conglomerate shadow of distal portions of the inus, and you should be able to see both of those structures pretty reliably.

Now you're seeing the round window, a niche, as in one of the posterior air spaces along the posterior wall.

Lateral to that you see the sinus symphony.

This is really a structure only important in that it's a place where disease can hide and is relatively inaccessible to the surgical examination.

And then lateral to that, you see the descending facial nerve canal.

And again, we'll review the facial nerve canal separately.

Here again, within the inner ear, I think we have a nice view of the basal turn of the cochlea with the middle and apical turns anterolateral to it.

Coronal Plane Anatomy

Now switching to the coronal plane, a fairly stereotypic anterior slice.

And again, our anterior oal is gonna be the malus.

And you're seeing the head, neck and the manubrium.

You can make out a very thin normal appearing tympanic membrane.

You don't need to see all of the tympanic membrane.

If it is abnormal and perforated likely it will be thickened.

You'll be able to see that.

You see the sputum.

And then between those structures, you see prussack space, not particularly important for trauma, but just a recognizable anatomic landmark, also called the lateral epi panic recess.

And then you see the two Cs, the carotid canal inferiorly and the cochlea anteriorly.

And that's a little mnemonic to remember that if you see the cochlea on a coronal image and you see a vascular channel beneath it, that's going to be the carotid canal, not the jugular.

Now you use the roof and the floor, the external auditory canal to divide the middle ear cavity into its various compartments.

And grossly any portion of the middle ear cavity that is superior to a line parallel to the roof of the external canal is in the EpiPen.

And that contains ossicles and air.

The meum is between those two lines.

And then the small and relatively unimportant hypo tendinum is inferior to a line draw parallel to the floor of the external auditory canal.

Now, if you look at a approximately midsection in the coronal plane, again, some fairly stereotypic structures, it's easy to find the lateral semi-circular canal 'cause it juts out into the middle layer cavity.

And as you look inferiorly, you can see the intra and panic segment of the facial nerve.

You can always find that inferior to the lateral semicircular canal.

And then even more inferiorly have a really nice view of the oval window, and that's where the staes foot plate sits and where tra sound is transmitted from the circular chain to the inner ear structures.

Here we also can see the internal auditory canal.

And that's something that should be on your checklist of things that you look at when you examine these studies.

The teman is the roof of the tpa cavity, the teman and mastoid, the roof of the mastoid cavity.

And these are important structures to assess in the setting of trauma because defects in these related to fracture can create a communication between the intracranial compartment and the mastoid cavity.

Another coronal mid slice with windowing to emphasize the ASC chain shows you the very stereotypic check mark, the long process of the incus and the lenticular processes of the inus.

And these again, form a check mark, and it's a good thing to look for.

I think it's an easy thing to find.

And you can again see the oval window, facial nerve canal, and the lateral semi-circular canal.

On these slices, just to remind us the chain of events, the atic membrane vibrates, that vibrates the malus, the inus and the staes.

And this is that check mark structure that we're seeing so nicely on the coronal scan.

A posterior slice in the coronal plane.

I think that's where I really learned how to understand this anatomy and sort of triangulate in multiple planes because those posterior recesses that we saw previously, the sinus Simponi, and the facial recess, the round window niche, are all displayed on this coronal slice, but you kind of have to look for them.

So the more medial one is that round window niche.

And then as you move progressively, laterally, you see the sinus timi.

And then the second genu of the facial nerve canal, and the facial nerve is going to descend in this plane.

And then lateral to that is the facial recess.

So those three airspace, you can usually routinely find those on a coronal scan.

This is the styloid process.

And again, the descending facial nerve canal will exit the cranium in that location.

Facial Nerve Anatomy

So we'll now quickly review the facial nerve on an axial plane.

The facial nerve will come in through the IAC, make its first gen at the level of the Gena ganglion, and then dive postal laterally along the medial surface of the tympanic cavity.

It then hits its second genu.

And you're seeing the sinus ani again, medial to it.

And this would be the level of the second gen.

And then that where it makes it second dive.

In this case, it dives inferiorly, and you will see it on consecutive axial images as a kind of soft tissue diet.

It can be sometimes confused with an opacified mastoid.

But when you do see it in sequential images, you'll realize that it is in fact the descending facial nerve canal.

And of course, that's easier to see on the coronal scan.

So that's the basic course of the facial nerve.

Detecting Temporal Bone Fractures

So let's move to temporal bone trauma.

There are clues that a temporal bone fracture might be there.

I mean, we'd all like to believe that we examine every structure and incredible detail on every scan.

But sometimes we have to rely on clues to prompt us to make a special survey of the structure.

So obviously both intracranial blood and particularly blood that is around the mastoid as well as extra cranial blood.

So a scalp hematoma that's over either the occiput or the lateral part of the skull are clues that there may have been direct trauma to this region.

And we need to be very vigilant about looking for a temporal bone fracture.

And of course, the presence of air where air doesn't belong is always a good clue that there has to have been some way that that air was introduced.

And again, this can be intracranial air, typically in the middle fossa or the posterior fossa, or it can be extracranial air related to a fracture of mastoid air cell in a subgaleal location.

Distinguishing True Fractures from Pseudofractures

One of the challenges I think for temporal bone trauma is distinguishing true fractures from pseudo fractures.

There's so many just normal developmental lines in and around the temporal bone that many of these are easily confused with fractures.

And these can be suture sutures, fissures, or canals.

So let's look at some examples.

This is a bone window from a head ct, and that's often what will prompt these exams.

You know, the patient has had significant trauma, they have a head ct, and somebody notices that there is one of these clues, air where it doesn't belong or blood in a suspicious location.

So our astute resident he did see the air trapped in the nasopharyngeal recesses, but also noted these two air bubbles over there, which are really too lateral to be part of any portion of the aerodigestive tract.

And you can see it is in approximately to the styloid process.

And here you see the mastoid tip as well.

So the patient went on to have a temporal bone ct, and that did demonstrate that the patient had a longitudinal temporal bone fracture.

In another patient two areas of air, both intracranial and extracranial air, so air in the middle fossa and then extra cranial air, similar in location to the scan I just showed you.

The temporal bone has abnormal soft tissue density within it, of course, not specific, but in the setting of trauma needs to make you think about the possibility of this represents hemo teum.

And then this patient went on to have a tera bone study with a complex fracture in hair.

You can see those intracranial air bubbles and then an associated intracranial hemorrhage again.

Both clues at that fracture existed.

Now this is an interesting case.

This is another case read on call by the residents, you know, just bone windows from a head ct and the resident was a student enough, again, to pick up the fact that there was a pneumo labyrinth.

So there was an abnormal focus of air within the cochlea.

And I think if you look at a lot of head cts and bone windows, you will notice that sometimes you get a spurious appearance of air.

It's a beam hardening type of artifact, but in this case, it did turn out to be real.

Now, that of course, is air in the wrong place and a clue that a fracture might be present, but actually it Doesn't mean that a fracture is necessarily present.

And we'll revisit this case a little bit later and discuss how that might happen.

So again, you know, so many lines in around the temporal bone, it's can be very difficult to differentiate between some of these and fractures.

Obviously, looking for corticated surfaces is very helpful.

And if of course you are an expert on the various fissures and canals and sutures that occur around there, and you can recognize them for what they are, that's great.

But luckily for us, these structures are almost invariably symmetric.

So you can use just looking at the other side.

The other side is your friend to help distinguish normal structures from those that are abnormal.

This singular canal, which transmits the posterior amary nerve to the posterior semi-circular canal, is one of the most frequently called I think, fractures by people who are somewhat inexperienced with looking at these cases.

It's obviously hard to see a corticated surface, especially since this is going through the very dense otic capsule bone.

And in fact the astute resident who did pick up this pneumo labyrinth called the singular canal fracture and failed to notice that the same line existed on the other side.

And in fact, this patient did not have a fracture.

And again, we will revisit this case one more time.

Temporal Bone Fracture Classifications

So let's talk about temporal bone fracture classifications.

I think everybody's familiar with the traditional transverse versus longitudinal versus mixed or complex, and these are very useful and they're very anatomically descriptive.

I think if you say there is a longitudinal fracture through the temporal bone, the clinician or whoever reads it, we'll have a starting idea of where the fracture is oriented.

And I think it is very useful.

However, it turns out that there are other ways of describing fractures that are more clinically relevant.

So in particular, if you describe the fracture as either violating or sparing the otic capsule you have, you have performed a classification scheme of significant clinical relevance.

So in patients who have otic capsule violating fractures, there's a fivefold increase in facial nerve injury.

There's a 25 fold increase in sensory neural hearing loss, and an eightfold increase in the incidence of CSF leak.

So that's a very useful fracture classification scheme.

So what I would suggest, and the way I do it is I give two classifications.

You're not limited to saying this is a horizontal or longitudinal fracture or otic capsule sparing or violating.

I'll say this is a horizontal, a longitudinal fracture that is otic capsule sparing.

And I've used both classifications scheme, I've given them a nice anatomic descriptor of what the fracture looks like, and I've also given them some information of clinical relevance, the features apex sparing and violating.

I don't think that's really taken off.

You'll see it occasionally in the literature.

But I think the otic capsule is probably the more used one of those terminology.

So working with that anatomic description, most fractures turn out to be longitudinal.

This occurs when there is a lateral blow and often is associated with a fracture of the squamal portion of the temporal bone, and the portion of that contributes to the calvarium.

These typically do spare the otic capsule, so that's a good thing.

In these patients, the incidence of conductive hearing loss exceeds sensory neural hearing loss, which makes sense because the otic capsule again, is spared.

But others structures are at risk.

So the TPA membrane clearly that is often involved in longitudinal fractures.

The ossicular chain, the facial nerve canal, the carotid canal, and the roof of the tpa cavity, the teman tippe are all at risk.

And I'm remember that the TMJ lives right underneath and can be involved in these fractures.

And these patients can present with trismus as a sign of possible temporal bone fracture.

So here's a pretty classic longitudinal fracture.

It's oriented along the long axis of the temporal bone.

You can see it going through the temporal squam through the mastoid cavity through the middle ear and then actually heading towards the carotid canal over here.

And then the ate region, the region of the first genu of the facial nerve is at risk in this particular fracture.

Less frequent r transverse fractures about 20%, and these occur from an occipital impact.

So somebody falls off a ladder and smacks the back of their head.

And the way I like to think about it's it kind of shears the petre apex off from the rest of the temporal bone.

So in these patients, there's a much lower incidence of typa membrane rupture because these fractures don't ever really go out through those lateral structures.

However, facial nerve injury is very common.

There are several points that the facial nerve can be injured, although the ICT remains the area that is the most susceptible.

It's just an area of weakness along the anterior margin of the temporal bone, because the bone, as you see, is not intact in that location.

In these patient, it is more common to have sensory neural hearing loss than a conductive hearing loss.

And that can be through fractures of the otic capsule.

So through the labyrinthine structures, a cochlear vestibule or through the internal auditory canal, as is demonstrated in this image.

So here's a patient with a transverse fracture.

The patient has some pneumo labyrinth.

You can see some abnormal air bubbles in the patient's vestibule.

And here is this fracture.

It's kind of shearing off the petre apex.

Again, I think it's kind of a useful construct.

And it is potentially hitting the facial nerve in probably its intra panic course.

Many of these fractures cannot be neatly compartmentalized.

In those cases you can call them mixed or oblique or complex.

This particular fracture looks like it wanted to be a longitudinal fracture, but then changes mine and dove posteriorly to become a transverse fracture.

And in those cases, I just try to be descriptive, you know, I'll say it goes out to the cortex follows along axis through the mastoid air cells and the sympa cavity, and then changes its course.

And in this case it goes actually across the internal auditory canal and the basal turn of the cochlear.

So this is a longitudinal mixed otic capsule violating fracture.

So important structures to look at when you are mapping fractures and when you are reporting fractures really have to do with things of functional importance.

So the otic capsule, obviously, of significant functional importance in terms of hearing facial nerve canal facial parsis is a very devastating complication of facial nerve fracture.

The internal auditory canal ossicles, again, the teman, the roof of these typa cavities.

Any place where the mastoid abuts the intracranial compartment is an important area to scrutinize because of the incidents potentially of CSF leak or the opposite complication extension of mastoid contents into the intracranial compartments potentially causing infection, and then of course, the carotid canal.

Associated Injuries and Complications

So let's look at what these complications are and why they're particularly important structures to look at.

Facial Nerve Injury

So, facial nerve injury again, is a potentially devastating complication.

It occurs more frequently in transverse fractures.

About half of patients with transverse fractures will have facial nerve injury, but it does occur in a significant percentage of people with the more common longitudinal fractures.

Again, it's most common in the geniculate region because that area is an area of developmental dehiscence of the temporal bone, of allowing that gula ganglion.

And then the greater superficial petrosal nerve, which comes off of that ganglion and heads towards the region of the cavor sinus.

That canal is just a natural area of dehiscence there.

Now, fist nerve injury occurs along a spectrum.

Obviously the most de the devastating one would be complete transection, although that can be repaired with grafts.

The prognosis is relatively poor.

And then sometimes it can really just be contused, stretched and concussed and function will recover.

So because of that, most of these are treated conservatively.

And then if nerve degeneration is demonstrated on studies, then the patient may be taken to the or for either a decompression or grafting.

So here's an example of a transverse fracture through the facial nerve canal.

This is actually a chronic fracture.

You can see that the margins are well sort of corticated, they're widened.

There is no hemo tipin, there's no swelling.

So this is not a new fracture.

And here you can see the facial nerve canal drawn out.

And this fracture potentially hits the facial nerve either in the fundus of the IAC or at the ict.

So several potential sites of facial nerve injury.

And this patient did have facial parsis following trauma.

In another patient again, a transverse fracture.

The fracture again, you can see is going through the labyrinth, but if we draw out the facial nerve canal, you can see that this likely hits the fracture in its proximal intra and panic segment, or at the level of the ict.

Hearing Loss

So hearing loss is obviously an important complication.

Conductive hearing loss is extremely common in the acute setting, but most commonly represents just hemo teum.

So if your ear is filled with blood, you don't have normal transmission of the sound through the assc chain.

And you won't hear that well.

And but that should obviously resolve.

If conductive hearing loss persists after the hemo tippen clears up, then you really need to look very carefully for a injuries.

Most ossicular injuries represent dislocations and they are dislocations at the inco dost pedial joint, inco malleolar joint, and these stiped vestibular joints.

So the inus being the largest and most complex, and the middle osci is the most susceptible to dislocations from its adjacent scis.

These are very hard to see.

I will show you an example, but I think with as we improve our scanning techniques and our spatial resolution, we're able to see more and more of these.

Ossicular fractures do occur, although they are less common and most frequently do involve the incus.

And this just showing you the appearance of hemo teum.

So one of the more common ones, and probably the easiest to recognize is the dislocation between the inus and the malus.

So on the normal side, we have the normal appearance of the ice cream cone, the malus head sitting on the body and shore process of the inus.

And on the abnormal side, you can see the clue of hemo teum.

And then if you look very carefully, there's just very subtle offset, and it can often be extremely subtle.

There's a little bit of widening of the joint relative to the other side, and the malus head is laterally offset, and I think you can appreciate that on the coronal image as well.

So the ice cream has fallen off and everybody's pretty sad.

This patient actually did recover good hearing.

The dislocation between the staes and the vestibule.

So essentially what we're talking about is the stapes foot plate is offset off of the oval window.

That's a rough diagnosis to make.

As Doug says, you gotta be pretty full of coffee to make that diagnosis, I think, and you gotta have a technically near perfect scan.

But this patient did have a prospectively diagnosed SVJ, so Edo vestibular joint dislocation.

And here you can see the, or you can imagine that, you can see the staes anterior and posterior cura.

This is the level of the oval window.

Here's the normal side, and the anterior and posterior cura are sitting well set on the level of the oval window.

And that is really the finding that you're looking for.

So here I've sort of indicated where the oval window is, and you can see that the stapes is posteriorly dislocated relative to that level of the oval window.

Here's again, the oval window on the contralateral side with the stapes normally located.

And just to show you on a better image in a patient who was able to cooperate for a better scan, the stapes anterior and posterior CRO should really be located perfectly in the middle of the oval window.

And that is the kind of subtle finding that if you make it, I think it's really great.

This patient had the bonus of having an additional fracture of the incus at the level of the junction of the long and lenticular processes.

Some of these dislocations are easy diagnoses to make.

So normal ice cream cone on the left and a completely disorganized joint with offset of the head from the body of the incus.

This is just the same patient on the coronal scan showing you the short process of the incus really abutting the sputum.

So completely dislocated.

Sensory neural hearing loss occurs in a significant percentage of patients with temporal bone trauma.

Again, it is more frequent in those transverse fractures which go through the otic capsule and go through the internal auditory canals.

There's a variety of causes, ranging from again, an injury to the Otic capsule, the cochlear vestibule, the IAC, but also to the brainstem.

And in patients with severe head trauma that can occur.

The other entity that can give you sensory neural hearing loss is perim fistula.

We'll get to that in a minute.

You can actually have a concussion that may result in intra labrinth and hemorrhage, which even in the absence of a fracture.

So you can have blood within your labyrinth, membranous labyrinth, and that can lead to secondary labyrinthitis, oci hands and longstanding hearing loss from that.

Remember, labyrinthitis Pacific hands is the endpoint of a variety of bad stimuli, infection, and blood being one of them.

Certainly a fracture, as in this case, that goes demonstrably through the structures of the OTA capsule through the labyrinth is at high risk.

And this patient did develop abnormal calcification in the basal turn of their cochlea labyrinthitis acidic hands, a long-term sequela.

Vertigo

Vertigo happens in about 50% of patients with significant head trauma.

And it's one of those concussion sort of findings as well.

Again, a spectrum of causes ranging from brainstem injury to labyrinthine concussion to mere syndrome, which can occur following trauma as well.

And again, perim fistula.

Perilymph Fistula

So let's talk about perim fistula.

This occurs when there is an abnormal communication between the membranous labyrinth either at because of rupture at the oval or round window and the middle ear cavity.

So essentially you have a fistula with which leakage of peri lymph into the middle layer cavity.

These patients are clinically difficult to diagnose.

It's a odd sort of composite of syndromes of symptoms.

And it can be a difficult clinical diagnosis, but often they have vertigo, fluctuating sensory, neural hearing loss, tinnitus and headache, all very non-specific symptoms.

You really have to work hard to put them together.

Radiographically it's even harder.

All you need, what you may see in its entirety is just fluid at the level of the oval or wound window in a patient with Pneumo labyrinth.

I'm not suggesting that anybody should suspect this diagnosis unless there is an additional strong clue like Pneumo Labyrinth.

So going back to that first case that I showed you where the resident astutely picked up the Pneumo Labyrinth, mistakenly called a singular canal fracture.

Here is an axial image from the temporal bone study, again confirming the Pneumo labyrinth.

And then the patient was ultimately noted to have fluid at the level of the oval window.

You can see, again, see the Pneumo labyrinth.

And this was a surgically proven perim fistula.

So the clue was the pneumo labyrinth.

And then the secondary finding was the fluid at the oval window.

If everybody can put everything together, you may be able to suspect this, and obviously it needs to be proven surgically.

CSF Leak and Meningitis

CSF leak in meningitis occurs in almost half of patients with significant temporal bone trauma.

Again, typically secondary to fraction of fracture of the temane.

So that interface between the intracranial compartment and the mastoid, and more frequent longitudinal fractures.

So obviously seeing fluid density on a CT study in the middle layer cavity is very nonspecific.

It can be an effusion, it can be hemo, teum way more frequently than it is A CSF leak.

But in some cases there will be a CSF leak.

Most of these will luckily close spontaneously, but a small percentage of them will need to be repaired.

And these patients can have the delayed complication of meningitis from that abnormal communication between the middle ear and the mastoid cavity and the intracranial compartment.

So here's an example of a teman fracture.

Nothing better than seeing air in the wrong place to prove to you that there is an abnormal communication, right?

They had to get there some way.

Brain and Vascular Injury

And finally, brain and vascular injury.

Remember that these patients have had significant enough trauma to fracture their temporal bone.

So about a third of them will have significant brain or vascular injury.

Subarachnoid hemorrhage, subdural epidurals, contusions, and DAI carotid canal fractures.

When I was training, we were doing an conventional angiography on all of these patients.

I think we've calmed down a little bit about this entity.

Patients probably should have a vascular study, but a CTA is probably good enough to rule out the sort of intimal injuries that and maybe pseudo aneurysms that can occur in the setting of this kind of trauma.

Again, the presence of air where it doesn't belong is a great clue.

So here's a fracture through the carotid canal with air within the carotid canal, proving that that fracture actually happened.

So here's a patient with air in the wrong place, subgaleal air, and a big hematoma was on, went on to have a documented longitudinal temporal bone fracture.

And then on his head ct, note the small conico injury.

So remember to assess very carefully the intracranial structures opposite from where the trauma occurred.

Summary

So in summary, make sure that your scans are technically appropriate.

You should really see the staes, look at the right and left temporal bone separately.

Look at small field of view studies, optimize things.

'cause these are really hard, I think, to look at.

Look at the right and left side to try to avoid the pitfall of all these pseudo fractures.

And then have an internal sort of checklist for the most important structures that are potentially injured in the setting of trauma.

Otic capsule, facial nerve canal, carotid.

And then don't forget to look at your soft tissue windows for the significant intracranial injuries that can occur.

So thanks for your attention.